Results of first coating tests with PET are in. I coated NaOH prepared test strips (10% solution) from the veggie container PET and Dura-lar with an 8% gelatin with red food dye added. Other than the NaOH treatment, there was no additional subbing done.
Coating was simple, I just dipped the strips in the container of gelatin and made sure to coat both the treated and untreated part of the strip. This was straight gelatin - no hardener or anything. After drying, the strips were suspended in 68 F water for 10 minutes. Gelatin on the treated part of the strip stayed put. On the untreated part the gelatin showed frilling. (I would hazard a guess that gelatin on the treated part of the strip was holding it in place.) No observable red dye in the water.
This has been my standard test and showed failure of the PVC and acetate base in the past and success of the CTA, melinex and 3M films. If the gelatin stayed put on the PET, I have some confidence it will work.
Time to get more serious. If I have time tomorrow I think I will melt some emulsion and try this for real.